The purpose of this study is to measure changes in ureagenesis after gene therapy in patients with OTC deficiency, an inborn error of urea synthesis. Current treatment is unsatisfactory. A Phase I study of adenoviral mediated gene therapy is underway. We are a collaborating insititution and wish to 1) perform heavy isotope/allopurinol studies to measure efficacy of the experimental treatment; and 2) to obtain blood for liver, renal, hematologic, and immune function to study safety.